You are right that the Accord grommets may be the way to go.
I was just trying to see what hotrod builders use and find out if there are other sources for grommets.
I believe the Accord has one grommet with two holes for evaporator & a second similar for the heater core.
Two smaller holes would be easier to drill, than one larger hole, but a single grommet with two holes may make install easier.
Thanks